Bestseller Cussler recycles plots and villains from earlier books in the sixth Fargo novel (after 2013’s Mayan Secrets), his first with coauthor Blake (Jet). In Spain, treasure hunters Sam and Remi Fargo run afoul of an old adversary, the thief Janus Benedict, while exploring the wreckage of a 17th-century ship. After beating Janus at his own game, the Fargos are off to the coast of Baffin Island, where they discover a Viking longship frozen in the ice. The ship is carrying perfectly preserved pre-Columbian artifacts, which lead the duo to Mexico to search for the tomb of the legendary Quetzalcoatl. In the tomb, they hope to find the Eye of Heaven, a flawless emerald the size of a grapefruit. Meanwhile, Benedict gets on their trail. Readers can expect the usual Fargo fun, though they should also be prepared for more clichéd prose than usual (e.g., “ ‘Truer words were never spoken,’ Sam agreed”). Agent: Peter Lampack, Peter Lampack Agency. (Sept.)